The Keysight U2903A is an accessory compatible and recommended to be used with the U2600A Series USB used with the U2600A USB Modular Digital I/O modules. The pin-outs of the U2903A is dependent on the USB Modular Digital I/O module that it is working with. For more information, please refer to the data sheet or the user guide of the USB Data Acquisition unit that U2903A is to be used with.